Hume-Rothery Symposium: Thermodynamics, Phase Equilibria and Kinetics for Materials Design and Engineering: CALPHAD and First Principles
Sponsored by: TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Integrated Computational Materials Engineering Committee
Program Organizers: Carelyn Campbell, National Institute of Standards and Technology; Michael Gao, National Energy Technology Laboratory; Wei Xiong, University of Pittsburgh
Monday 2:30 PM
February 24, 2020
Room: 32A
Location: San Diego Convention Ctr
Session Chair: Michael Gao, National Energy Technology Laboratory; Raymundo Arroyave, Texas A&M University
2:30 PM Invited
A Hexagonal Close Packed Multi-principal-element Alloy Identified Computationally: Axel van de Walle1; Ruoshi Sun1; Qijun Hong1; Julian Sabisch2; Andrew Minor3; Mark Asta3; 1Brown University; 2Sandia National Laboratory; 3University of California, Berkeley
In this work we have considered the design of alloy solid solutions that can mimic the excellent combination of mechanical properties displayed by elemental rhenium, but with reduced cost. Based on consideration of deformation mechanisms in rhenium, we develop a design principle that trades off average valence electron count and cost considerations, identifying a promising pool of candidate substitute alloys: the Mo-Ru-Ta-W quaternary system. We demonstrate how this picture can be combined with a computational thermodynamics model of phase stability, based on high-throughput ab initio calculations, to further narrow down the search and deliver alloys that maintain rhenium’s desirable hcp crystal structure. This thermodynamic model is validated with comparisons to known binary phase diagrams sections and corroborated by experimental synthesis and structural characterization demonstrating multi-principle-element hcp solid-solution samples selected from a promising composition range.
3:10 PM Invited
First-principles Thermodynamics of Refractory Alloys and their Oxides: Anton Van der Ven1; Naga Sri Gunda1; Anirudh Natarajan1; 1University of California, Santa Barbara
Alloys containing group IV, V and VI refractory elements exhibit a rich variety of phases and intermetallic compounds. Refractory elements are unique in the way they interact with carbon, nitrogen and oxygen. Elements such as Ti, Zr and Hf are capable of dissolving very high concentrations of oxygen as interstitial species. Though not as extreme, other refractory elements such as V, Nb and Ta are also able to dissolve non-negligible concentrations of C, N and O. The ease with which refractory elements can dissolve interstitial species complicates experimental characterization of phase stability of refractory alloys. First-principles statistical mechanics approaches are able to shed light on the effect of dissolved interstitial species on phase stability and short-range ordering phenomena. In this talk we will describe how variations in oxygen chemical potentials can dramatically alter the phase diagrams of alloys containing refractory elements, even under reducing conditions.
3:50 PM Invited
On the Intrinsic Alloying Behavior in the A and M Sublattices of MAX Phases: Raymundo Arroyave1; Anjana Talapatra2; Thien Duong3; Miladin Radovic1; 1Texas A&M University; 2Los Alamos National Laboratory; 3Argonne National Laboratory
In this talk, I will present recent results in which the intrinsic alloying behavior of the M and A sublattices in some prototypical 211 and 312 MAX Phases has been investigated from first-principles. Specifically the energetics of the configurational space in these systems is explored through cluster expansions in which the energy of arbitrary configurations is parameterized in terms of their constituent pairs, triples, tetrahedra, etc. This extensive study has already yielded significant insights into the intrinsic alloying trends of several systems: while in some cases there are clear tendencies towards strong ordering, in other cases there are equally strong tendencies towards phase separation, with a sizable fraction of the systems studied exhibiting almost ideal mixing. Observed trends are rationalized in terms of the underlying changes in the electronic structure of the compounds. The alloying trends are also discussed interms of their relevance for yet undiscovered MAX solid solutions.
4:30 PM Break
4:50 PM Invited
Thermodynamic Modeling of Precipitates of Topologically Close-packed Phases: Thomas Hammerschmidt1; 1ICAMS Ruhr-University Bochum
The precipitation of topologically close-packed (TCP) phases in superalloys is highly undesirable due to the detrimental effect on the mechanical properties. The structural stability of bulk TCP phases in thermodynamic equilibrium is well understood but little is known about the dominating factors that govern the formation of TCP phase precipitates within a superalloy matrix. Here, a thermodynamic modelling approach of the TCP phase precipitates is presented. It connects the experimentally observed local chemical composition with empirical maps of bulk TCP phase stability and with solidification modelling based on CALPHAD databases. Several examples for Ni-base and Co-base superalloys indicate that the precipitates exhibit chemical compositions that are expected to form a TCP phase also as bulk material. An example of the limits of this purely thermodynamic interpretation is the stress-induced formation of TCP phases that was observed recently in low-cycle fatigue tests of a Ni-based superalloy.
5:30 PM Invited
Alloys, Processing, Applications, Models and Software: The Wide Domain of Gibbs Energies Sets Giving Impulse to Invention: Suzana Fries1; Sara Catalina Pineda Heresi1; Daniela Ivanova1; Uzair Rehman1; Silvana Tumminello2; 1Ruhr-Universität Bochum; 2German Aerospace Center
Alloys by design, Additive Manufacturing, Thermoelectric Energy Conversion, Effective robust models connected to First-Principles, Open Gibbs energy minimizers are the items we expose in this contribution. Along the years the use of Gibbs energies sets describing thermodynamic equilibrium extended in such a way that alloy properties can be ad hoc designed and processes that include metastable states can be followed and optimized. Properties depending of alloy composition can be tuned. The inclusion of the electronic structure in the models brought the extrapolations to true predictions and new computational strategies allowed the fast use of concise and selected information in simulations of microstructures and continuum. All that evolution happened in the last 30 years and it is accelerating in the recent time, anticipating a development of materials science beyond the imaginable at the end of the last century. As a testimony of that facts, surrounded by scientists being formed in this environment, a report is given.